1. Field of the Invention
The present invention relates to a fuel cell system and method and, more particularly, to a fuel cell system and method that is highly responsive to varying loads.
2. Description of the Related Art
A fuel cell system including an evaporator as shown in FIG. 1 has been investigated by the present inventors.
In FIG. 1, an evaporator 1 includes a cross type heat exchanger 2. The cross type heat exchanger 2 includes a first cross type heat exchanger 3 for vaporizing water to generate steam ST, and a second cross type heat exchanger 4 for vaporizing methanol to produce methanol vapor MV.
The first cross type heat exchanger 3 includes a heat exchanging chamber 3a, a plurality of water injection nozzles 3b adapted to be supplied with the water from a water tank 5 via a water feed pump 6, a water dispersion panel 3c on which water is accumulated, and a heat exchanger section 3d disposed at an intermediate area of the heat exchanging chamber 3a. 
The heat exchanger section 3d communicates with a combustor 7 to receive heating gas exhausted therefrom for generating the steam ST by heating water FW with heating gas HG. The combustor combusts air AR and fuel F1 to produce the heating gas HG. The steam ST is then supplied to a reformer.
Likewise, the second cross type heat exchanger 4 includes a heat exchanging chamber 4a having a plurality of methanol injection nozzles 4b adapted to be supplied with methanol from a methanol tank 8 via a methanol feed pump 9, a methanol dispersion panel 4c, and a heat exchanger section 4d communicating with the combustor 7 to receive the heating gas HG for generating the methanol vapor MV, that is supplied to the reformer.
In such an evaporator employed in the fuel cell system discussed above, however, feed water is sprayed onto the dispersion panel 3c by the water injection nozzles 3b and is supplied to an evaporating heat transfer surface of the heat exchanger section 3d. With such a structure, a certain time interval is required to accumulate feed water on areas above the dispersion panel 3c and, therefore, a delay time exists before a necessary amount of steam is obtained. Such a situation is the same as in the case that a necessary amount of methanol vapor is to be obtained.
The present invention has been made in view of the inadequacies as above investigated and has an object to provide a fuel cell system and method which overcomes and eliminates such inadequacies, that is, to provide a fuel cell system including an evaporator which is highly responsive to varying loads of a vehicle and method therefor.
To achieve the above object, a fuel cell system of the present invention is provided with a fuel cell generating electric power; a combustor producing heating gas; an evaporator including an evaporating heat transfer surface evaporating fuel with the heating gas to produce fuel vapor, the evaporator including a liquid sump section located in the vicinity of the evaporating heat transfer surface and having a variable volume; a volume control device associated with the liquid sump section to control the volume thereof such that a demanded amount of the fuel vapor is obtained; and a reformer reforming the fuel vapor to produce reformed gas. Here the fuel cell is supplied with the reformed gas and a gas containing oxygen to generate the electric power.
In other words, a fuel cell system of the present invention is provided with a fuel cell generating electric power; a combusting means for producing heating gas; an evaporating means for evaporating fuel with the heating gas to produce fuel vapor, the evaporating means including a liquid sump section located in the vicinity of the evaporating heat transfer surface and having a variable volume; a volume control means, associated with the liquid sump section, for controlling the volume thereof such that a demanded amount of the fuel vapor is obtained; and a reforming means for reforming the fuel vapor to produce reformed gas. Here, the fuel cell is supplied with the reformed gas and a gas containing oxygen to generate the electric power.
Beside, a controlling method of a fuel cell system of the present invention produces heating gas; evaporates fuel in a liquid sump section of the fuel cell system with the heating gas to produce fuel vapor, while controlling a volume of the liquid sump section such that a demanded amount of the fuel vapor is obtained; reforms the fuel vapor to produce reformed gas; and supplies the reformed gas and a gas containing oxygen such that the fuel cell generates electric power.
Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of the invention, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention in general terms. Incidentally, like numerals refer to like parts throughout the disclosure.